The demand for inexpensive microelectronic devices has resulted in the development of organic materials potentially useful in electronic and optoelectronic systems. This has led to advances in microelectronic devices that make it possible to inexpensively produce microelectronic devices that occupy large areas and are easily fabricated on rigid or flexible plastic supports. These advances include the development of conducting, semiconducting, and dielectric organic materials.
Unfortunately, present methods for patterning these organic materials are less than adequate. One such method is screen printing. See, Z. Bao, Y. Feng, A. Dodabalapur, V. R. Raju, A. J. Lovinger, "High-performance Plastic Transistors Fabricated by Printing Techniques," CHEM. MATER. 9 (1997) at 1299-1301. But the use of screen printing in making microelectronic devices such as FETs is limited by relatively poor resolution (.about.100 .mu.m) of the screen printing method.
Another method which is capable of generating microstructures in a wide range of materials with feature sizes between one and several hundred microns is micromolding in capillaries (MIMIC). MIMIC involves forming capillary channels between a support and an elastomeric mold that contains recessed channels that emerge from the edges of the mold. A solution containing a solvent and a material (MIMIC solution) which forms the microstructure is applied to the channels at the edges of the mold. Once the solvent in the MIMIC solution evaporates, the mold is lifted from the substrate leaving a microstructure composed of the material. GaAs/AlGaAs heterostructure FETs with dimensions as small as .about.20 .mu.m have been fabricated using MIMIC defined sacrificial polymer layers. The MIMIC defined polymer layers were used in "lift-off" procedures to form the gates and the electrodes of the FETs.
The conventional MIMIC technique, however, has several serious disadvantages. First, the conventional molds used in MIMIC may only be filled by repeatedly applying the MIMIC solution to the recessed channels at the edges of the mold as the solvent in the solution evaporates. Second, when a conventional MIMIC mold is removed, excess unusable material remains on the substrate where the edges of the mold were located. This material must then be removed by cutting it away from the substrate. Third, the MIMIC solution may have to travel a greater distance in an edge filled MIMIC mold which leads to very long filling times. Fourth, patterns made from more than one type of material are not possible with conventional MIMIC molds. Fifth, MIMIC molds can not be easily integrated with conventional printing methods such ink jet printing or screen printing. Sixth, the MIMIC solution can not be forced or drawn into a conventional MIMIC mold with a pressure or a vacuum.
Accordingly, there is a need for an improved mold for use in MIMIC that overcomes the deficiencies of conventional MIMIC molds.